Abstract
The aim of the study was to develop routine procedures for the isolation and cultivation of the actinorhizal symbiont Frankia. Optimum isolation of the Frankia endophyte was achieved using selective filtration or serial dilution of nodule homogenates. A total of 15 strains were isolated that satisfied Koch's postulates. Techniques were developed for the purification and preservation of Frankia strains. Overall Frankia growth is slow compared to other actinomycetes. Screening of carbon and nitrogen sources demonstrated that Tween 80, propionate, pyruvate and trehalose were optimum carbon sources and ammonium chloride, ammonium nitrate, glutamate and aspartate, optimum nitrogen sources. 15N studies were carried out to elucidate the pathways of nitrogen metabolism in Frankia. The efficiency of nitrogen fixation was determined. Propionate at a concentration of 0.47g/1 was the optimum carbon source for growth and yield in Frankia. Substrate utilisation was measured in batch culture for the first time. Propionate was shown to be an inhibitory carbon source using a single substrate model. Ki, Ks and S crit were calculated in batch culture. The single substrate inhibition model was used to predict the outcome of a mutation and selection programme to obtain propionate tolerant mutants. Storage and mobilisation of trehalose was demonstrated in Frankia. A model was proposed to explain phasic growth events in Frankia, as a result of this mobilisation. Limited screening studies for bioactive secondary metabolites were carried out.